Iodoform
Iodoform, also known as triiodomethane (CHI₃), is a pale yellow, crystalline organoiodine compound with a molecular weight of 393.73 g/mol, notable for its distinctive saffron-like odor and volatility.[1] It appears as a bright yellow powder or crystals, melts at 119–122 °C, sublimes at 218 °C, and exhibits low solubility in water (<1 mg/mL) but good solubility in organic solvents like ethanol, ether, and chloroform.[1] Discovered in 1822 by French chemist Georges Serullas through the reaction of iodine vapor with steam over red-hot coals, iodoform's antiseptic properties were identified in 1880, leading to its widespread adoption in medical practice during the late 19th and early 20th centuries. It gained prominence as a disinfectant due to its ability to slowly release free iodine, which denatures bacterial proteins and exhibits mild antimicrobial activity without significant irritation.[2] Historically, iodoform served as a key antiseptic in surgical and dental applications, including wound dressings, cavity packing for conditions like dry socket, and formulations such as Whitehead's varnish (introduced in 1891) and bismuth iodoform paraffin paste (BIPP, developed in 1916 for World War I wound care).[3] It promotes granulation tissue formation, destroys microbial toxins, and remains stable in oral fluids and blood, making it suitable for secondary wound healing in ulcers, cysts, and postoperative sites when mixed with agents like glycerine or eucalyptus oil.[2] In chemistry, iodoform is central to the iodoform test, a qualitative reaction used to detect methyl ketones or alcohols that can be oxidized to methyl ketones, producing the characteristic yellow precipitate.[1] Although its use has declined since the mid-20th century in favor of safer, more effective antiseptics due to potential toxicity—including skin/eye irritation, allergic reactions (1–12% incidence), and risks to the liver, kidneys, or fetus in pregnancy—iodoform persists in niche applications like ENT surgery, neurosurgery, oral/maxillofacial procedures, and veterinary disinfectants for lesions.[1][3] It is synthesized industrially from acetone, sodium hypochlorite, potassium iodide, and sodium hydroxide, and is classified as harmful if swallowed or inhaled but non-carcinogenic.[1]Nomenclature and structure
Nomenclature
Iodoform is the retained trivial name for the organoiodine compound with the molecular formula CHI3.[4] The term "iodoform" originates from the prefix "iodo-" denoting iodine combined with "-form," derived from "formyl," referring to the formyl group (HCO–), reflecting its historical association with formyl derivatives.[5] This naming convention parallels the haloform series, which includes chloroform (retained name for trichloromethane, CHCl3), bromoform (retained name for tribromomethane, CHBr3), and iodoform as the trihalogenated methane analogs where chlorine, bromine, or iodine replaces hydrogen atoms.[4] The preferred IUPAC name for CHI3 is triiodomethane, emphasizing the systematic substitution of three iodine atoms on a methane backbone.[4] Other synonymous names include carbon triiodide and methyl triiodide, which highlight the carbon-iodine composition or the methyl group's implied structure.[1] These alternative designations are used in various chemical contexts but do not supersede the retained or preferred IUPAC nomenclature for formal identification.[6]Molecular structure
Iodoform has the chemical formula \ce{CHI3}.[1] The molecule features a central carbon atom covalently bonded to one hydrogen atom and three iodine atoms via single bonds. In its Lewis structure, the carbon atom serves as the central atom with four sigma bonds and no lone pairs, while each iodine atom possesses three lone pairs of electrons to satisfy the octet rule.[1][7] The three-dimensional arrangement adopts a tetrahedral molecular geometry with C_{3v} point group symmetry, where the central carbon is at the tetrahedron's center, the hydrogen occupies one vertex, and the three iodine atoms occupy the remaining vertices.[1][8] The C–I bond lengths are approximately 213 pm, and the H–C–I bond angle is about 109.5°, consistent with the idealized tetrahedral configuration.[9]Properties
Physical properties
Iodoform is a pale yellow to bright yellow crystalline solid or powder with a pungent, disagreeable odor often described as saffron-like.[1][10][11] The compound exhibits noticeable volatility at room temperature due to its vapor pressure of approximately 0.04 mmHg, resulting in a detectable vapor.[1][12] Key physical properties of iodoform under standard conditions are summarized below:| Property | Value |
|---|---|
| Molecular weight | 393.73 g/mol |
| Melting point | 119–122 °C |
| Boiling point | 218 °C (sublimes) |
| Density | 4.008 g/cm³ at 25 °C |
| Solubility in water | 0.01 g/100 mL at room temperature |
| Solubility in organic solvents | Soluble in ethanol (7.8 g/100 mL), diethyl ether (13.6 g/100 mL), and chloroform |